For a transistor in CE mode to be used as an amplifier, it must be operated in :

Options

A. Saturation region only
B. Both cut-off and Saturation
C. The active region only
D. Cut-off region only

Answer

To determine the correct operating mode for a transistor in common emitter (CE) configuration to be used as an amplifier, we need to analyze the conditions under which the transistor operates effectively in this mode.

### Step-by-Step Solution:

1. **Understanding the Common Emitter Configuration**:
- In a common emitter configuration, the transistor has three terminals: the collector (C), base (B), and emitter (E). The input signal is applied between the base and emitter, while the output is taken between the collector and emitter.

2. **Biasing the Transistor**:
- For a transistor to function as an amplifier, it must be properly biased. This involves applying a DC voltage to the base-emitter junction to ensure it is in the correct operating region.

3. **Forward and Reverse Bias**:
- In the common emitter configuration, the base-emitter junction must be forward biased, while the collector-base junction must be reverse biased. This allows the transistor to control a larger current flowing from collector to emitter based on a smaller current flowing into the base.

4. **Active Region**:
- The region where the transistor operates as an amplifier is called the active region. In this region, the transistor can amplify the input signal. It is essential that the transistor remains in this region to function effectively as an amplifier.

5. **Conclusion**:
- Therefore, for a transistor in common emitter mode to be used as an amplifier, it must be operated in the **active region**.

### Final Answer:
The transistor in common emitter mode must be operated in the **active region** to be used as an amplifier.

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